Centerless grinding machine



Aug. 6, 1935. A, Hl LLQYD 2,010,730

CENTERLESS GRINDING MACHINE Filed Jan. 30, 1955 Hill!!!Illlllllllllltllillllliil 'IHIIIIIIIIIIIIIIHIIIIIIIIIIII urZzur E lloyd 19%.,e-m., c MW,

' Patented Aug. 6, 1935 PATENT OFFICE CENTERLESS GRINDING MACHINE Arthur Harold Lloyd, Coventry, England Application January 30, 1935, Serial No. 4,166 In Great Britain April 12, 1934 12 Claims.

This invention relates to centerless grinding machines of the kind where the work-piece is supported on a ledge between an abradant surface on a grinding wheel and a backing wheel '5 and rotated relatively to the grinding wheel.

Preferably, though not necessarily, the grinding wheel is rotated relatively quickly and the backing wheel relatively slowly, the ledge conveniently being inclined away from the grinding wheel so that the work tends to be wedged by the grinding wheel between the ledge and the backing wheel; whereby the frictional contact of the backing wheel on the work causes rotation of the latter.

The main object of the present invention is to provide a machine of this kind for correcting screw-threads-ie., rendering them accurate.

A further object is to provide the grinding wheel with annular abradant ridges, preferably around its periphery, which mate with the screwthread of the work-piece and thus accurately grind it. The rotation of the work-piece will cause it to travel axially so that the whole surl face of the thread will be treated. The axes of the grinding wheel and work-piece should be set relatively to one another, in relation to the helix angle of the thread, such that the abradant ridges do not foul the thread.

According to a further feature of the invention, where the abradant surface on the grinding wheel is in the form of annular ridges adapted accurately to grind the screw-thread ofthe workpiece, the latter is caused to travel axially as it is rotated, so that the whole surface of its screwthread will be treated, by engagement with similarly-sectioned teeth formed on the supporting ledge. These teeth, however, are not essential in carrying out the invention.

In the accompanying diagrammatic drawing:-

Figure 1 is an outline end elevation of one arrangement according to the invention;

Figure 2 isa plan thereof;

Figure 3 a side elevation omitting the backing wheel; and

Figure 4 is a side elevation showing how the ledge is arranged for a headed piece of work, such as a bolt.

In the construction illustrated in Figures 1 to 3, where the work-piece I I has no part at the end of its screw-thread I2 of greater diameter than the minimum diameter of the screw-thread, i. e., than the bottom of the thread, the workpiece can be fed axially into position either by hand or gravity as by means of a chute. When entering between the wheels it is rotated by frictional contact with the backing wheel I3-which in this case is shown as rotating clockwise, in the direction in which the grinding wheel Il is rotating, the work-piece therefore being driven anti-clockwise. This rotation of the work-piece causes it to travel axially as soon as its screwthread has been engaged by any axially fixed teeth or the equivalent, such as by the abradant ridges I5 or by ridges on the backing wheel if the latter were so provided. The ridges I5 are formed between annular grooves I6 on the periphery of the grinding wheel, the ridges and grooves being of a section which is similar to two or three or more of the threads to be ground. In this way the whole surface of the screw-thread on the work-piece receives attention and the threads can be ground to the correct prole and pitch.

In many cases it is immaterial whether the backing wheel is provided with a corresponding mating thread or whether it has a substantially plain, ribbed or other periphery.A It is shown in the drawing as having a plain periphery.

In the actual construction illustrated, the axes I'I, I 1 of the grinding and backing wheels are parallel or nearly parallel to one another and the wheels are shown as being fast on shafts carrying, respectively, gear wheels I8, I9 in mesh through an intermediate gear 20. The ratios are such as to ensure that the grinding and backing wheels will be driven at appropriate speeds, the grinding wheel shaft being shown with a driving pulley 2|, though obviously it or the other shaft may be driven in other ways. Furthermore, in the present instance teeth 22 are shown on the surface of the supporting ledge 23, the teeth being shown as being cut straight instead of being of helical form (though this is not essential) so that there will be what is commonly termed point contact between the teeth and screw-thread of the work-piece II. The teeth on the ledge are of a section which is similar to a few of the threads of the work-piece I I. It is, in the present instance, the engagement of the work thread with these teeth, rather than with the ridges I5 on the grinding wheel, that causes the work to travel axially when rotated by the backing wheel. It will be evident that the teeth will4 not be continued alongthe ledge so far that the rotation of the work-piece, and in consequence its axial travel, will cease before the work-piece is clear of theteeth. In other words, when the Work-piece has been shifted axially, in the direction of the arrow (Figure 3), just clear of the backing wheel-in which case it will no longer be rotated-it must then be 66 clear of the teeth of the ledge. I do not claim, however, that the teeth of the ledge are essential. I

The ledge has its surface tilted so that the longitudinal center line of its inclined surface (parallel to the line 24 of Figure 3) vis inclined to the axis I1 of the grinding wheel. AFor operating upon left-hand screw-threads (as shown in Figures 1, 2, and 3) the ledge should be arranged so that the longitudinal center line of its surface rises in the direction to which the workpiece will be fed, i. e., sothat the work-piece will be fed uphill. For right-hand screw-threads the ledge is tilted so that the longitudinal center line of its surface rises in the other direction, i. e.,

yso that the work-piece will be fed` downhill. The

tilting is preferably such that the axis of the work-piece is inclined to that of the grinding wheel in a manner dependent upon the helix angle of the-screW-thread I2.

When the apparatus of the invention is used for dealing with a work-piece which has no part beyond its screw-thread of greater diameter than the minimum diameter of the screw-thread, as illustrated by Figures 1 to 3, the rotational axis of the backing wheel may in some cases be inclined slightly--for example, by as much as two degrees-to the axis I 1 of the grinding wheel;

I preferably being oppositely inclined to the center line of the ledge surface.

If desired, however, the work-piece lmay befed downwardly along the plane 21, at right-angles to the plane 25 which is near or contains the axes Il, I1 of' the grinding and backing wheels, and this is essential in those cases, as indicated by Figure 4, where the work-piece is a bolt or other piece having an end 28 of a diameter greater than the minimum diameter of the screwthread. In this case the arrangement is such that the grinding operation commences at the end of the screwthread of the work-piece nearer the enlarged end 28 and' such that the axial travel imparted to the work-piece is in the direction towards the enlarged end (to the left in Figure 4), so that the enlarged end is at all times kept clear of the grinding wheel. Obviously, in cases where the screw-thread runs up close to the enlarged end 28 the supporting ledge 23 will be cut away at the adjacent end of the teeth, as indicated at 29, to accommodate the enlarged end. Furthermore, in this case the two rotational axes Il, I l are definitely co-planar for preference.

Obviously, if desired, this latter form of machine may be used for grinding work-pieces having no end part of larger diameter than the minimum diameter of the screw-thread.

By means of the invention screw-threads of a given pitch can be corrected in a very simple manner independently of the diameter of the workpiece, provision being made for the movement of the rotational axes Il, I1 of the grinding and backing wheels towards and away from the ledge 23 as necessary for exerting the requisite pressure on the work-piece; but for a work-piece with a screw-thread of another pitch a different grinding wheel 'and ledge would have to be substituted, these having annular ridges and teeth, respectively, to mate with the screw-thread of this other pitch-that is, if a ledge with teeth on it were being used.

The invention is obviously not restricted to the treatment of cylindrical screw-threads as it may be adapted for taper screw-threads.

What I claim as my invention and desire to secure by Letters Patent of the United States 1. A centerless grinding machine, for the screwthread of a Work-piece, comprising a grinding wheel, a ledge and a backing wheel, these parts being arranged so that the work-piece can be supported on the ledge in contact with the grinding and backing wheels, means for rotating the grinding wheel, and means for rotating the backing wheel to rotate the Work-piece relatively to theggrinding wheel, the grinding wheel having annular abradant ridges which mate Lwith the screw-thread of the work-piece.

2. A centerless grnding machine, for the screwthread of a workiece, comprising a grinding wheel, a ledge and a backing wheel, said parts being arranged so that the work-piece can be supported on the ledge in contact with the wheels, means for eiecting rotation of the grinding wheel, means for eiecting rotation of the backing wheel to turn the work-piece relatively to the grinding wheel, the grinding wheel having abradant annular ridges which mate with the screw-thread of the work-piece, and the ledge having on its supporting surface similarly-sectioned teeth in mesh with the screw-thread.

3. A centerless grinding machine, for the screwthread of a Work-piece, comprising a grinding wheel, a ledge and a backing wheel, these parts -being arranged so that the work-piece can be supported on the ledge in contact with the wheels, the axes of said wheels being substantially coplanar, means for rotating the grinding wheel, and means for rotating the backing wheel to turn the work-piece relatively to the grinding wheel, the grinding wheel having around its periphery annular abradant ridges of a section similar to a few of the threads of the Work-piece and the supporting surface of the ledge being inclined so that the axis of the work-piece is inclined to the plane of the wheel axes dependent upon the helix angle of the screw-thread. A

(i. A centerless grinding machine, as claimed in claim 3, the inclination of the ledge being such that the work-piece, when caused to travel axially owing to its being rotated, will travel uphill if the screw-thread be a left-hand one.

5. A centerless grinding machine, as claimed in claim 3, the inclination of the ledge being such that the work-piece, when caused to travel axially owing to its being rotated, will travel downhill if the screw-thread is a right-hand one.

6. A centerless grinding machine, for the screwthread of a work-piece, comprising spaced grinding and backing wheels with their axes substantially co-planar, the grinding wheel having annular abradant ridges on its periphery which can mate with the screw-thread of the work-piece, a ledge for supporting the work-piece in contact with the Wheels, means for rotating the grinding wheel, and means for rotating the backing wheel and the contacting Work-piece at a different speed from that of the grinding wheel, the supporting surface of the ledge being tilted away from the grinding wheel and being inclined such that the inclination of the axis of the work-piece to the plane of the axes of the Wheels is dependent upon the helix angle of the screw-thread.

7. A centerless grinding machine, for the screwthread of a work-piece, comprising spaced grinding and backing wheels with their axes substantially co-planar, the grinding wheel having annular abradant ridges on its periphery which can mate with the screw-thread of the work-piece, a ledge for supporting the work-piece in contact with the wheels, means for rotating the grinding wheel, and means for rotating the backing wheel and the contacting work-piece at a different speed from that of the grinding wheel, the supporting surface of the ledge being tilted away from the grinding wheel and being inclined such that the inclination of the axis of the work-piece to the plane of the axes of the wheels is dependent upon the helix angle of the screw-thread, and the ledge having teeth which mesh with the screwthread.

8. A centerless grinding machine, for the screwthread of a Work-piece, comprising spaced grinding and backing wheels, the grinding wheel having annular abradant ridges of a section which is similar to a few of the threads of the workpiece, a ledge for supporting the work-piece in contact with the wheels, means for rotating the grinding wheel and the backing wheel with the work-piece in the same direction, the surface of the ledge having teeth which can mesh with the screw-thread of the work-piece.

9. A centerless grinding machine, for the screw-thread of a work-piece, comprising a grinding wheel, a ledge and a backing wheel, these parts being disposed so that the work-piece can be supported on the ledge in contact with the grinding and backing wheels, means for rotating the wheels, the supporting surface of the ledge being inclined away from the grinding wheel suchthat the frictional contact between the backing wheel and the work-piece will cause the rotation of the work-piece, and the grinding wheel having abradant annular ridges which mate with the screw-thread.

10. A centerless grinding machine; for the screw-thread of a work-piece, comprising a grinding wheel, a ledge and a backing wheel, these parts being relatively disposed such that the work-piece can be supported on the ledge in contact with the, wheels, means for rotating the wheels. the supporting surface ci' the ledge bei ing inclined away from the grinding wheel such that the frictional contact between the backing Wheel and the work-piece will cause the latter to revolve, the grinding wheel having abradant annular ridges around its periphery which mate with the screw-thread of the work-piece, and the ledge having similarly-sectioned teeth in mesh with the screw-thread.

11. A centerless grinding machine, for the screw-thread of a Work piece, comprising spaced grinding and backing Wheels, the grinding wheel having annular abradant ridges of a section which is similar to a few of the threads of the work'- piece, means for rotating the wheels in the same direction at different speeds, and a ledge for supporting the work-piece in contact with the wheels. the surface of the ledge being tilted away from the grinding wheel such that the work-piece will be rotated, in the opposite direction to that of the grinding "wheel, by frictional contact with' the backing wheel.

12. A centerless grinding machine, for the screw-thread of a work-piece, comprising spaced grinding and backing wheels, the grinding wheel having annular abradantridges of a section which is similar to a few of the threads of the workpiece, means for rotating the wheels in the same direction at different speeds, and a ledge for supporting the work-piece in contact with thewheels, the surface of the ledge being tilted away from the grinding wheel such that the work-piece will be rotated, in the opposite direction to that of the grinding wheel, by frictional contact with the backing wheel, and the. ledge having teeth which mesh with the screw-thread, whereby the work-piece is moved axially on being rotated.

ARTHUR HAROLD LLOYD. 

